This invention relates to the field of optical range mapping of the nontriangulation type.
In activities as diverse as midair refueling, automatic target recognition, robotic vision, space docking, industrial inspection and customized equipment design, for example, there is need for precise mappings of range measurements. Often such measurements are over distances in excess of that accommodated by conventional graduated tension member measurement or impractical of such measurement.
The term mapping in this description includes the concept of range determination for a multiplicity of different points located on the distal target object and therefore is inclusive of aspects relating to shape and size of the target object.
In the past, such techniques as triangulation using optical images taken from two different viewpoints, or the time for energy propagation to and from points on a distal target object have been employed for accomplishing range mapping measurements. In range mapping systems, however, there is often a need for such speed and accuracy and operational simplicity in determining range maps of a distal target as to preclude the use of previous measurement techniques. The triangulation range determination, for example, as is often used in cameras and in artillery measurement periscopes is slow and often cumbersome in range mapping accomplishment and somewhat difficult to perform automatically as a computer or electronics system operating function.
Since triangulation usually involves two superimposed or split field images for indication, it often requires the conclusion of a human interpreter to reliably complete the measurement. Another example of triangulation impracticability is to be found in the field of airborne weaponry wherein it is often difficult to separate a plurality of optical apertures by a meaningful distance on the limited confines of an airframe--and yet there is a strong need for quick and accurate measurement of range maps for use in rocketry and other weapons related functions.
Since many current uses for a range mapping system impose requirements of nonhuman interpretation, small physical size, the use of a single optical aperture, and accuracy in both the near field and far field environment, there is need in the art for an improved range mapping system such as the present "Laser Imaging and Ranging Systems Using Two Cameras" . Parenthetically, in view of this name and accomplished function, the system of the present invention can be conveniently referred to by way of the acronym LIMAR/2 which is based on the first or first and second letters of the words appearing in the name. The present document hereby incorporates by reference the above referred-to one camera laser imaging and ranging system patent document.
The patent art includes several examples of range mapping systems including laser operated systems which are of interest with respect to the present invention. Included in these patent examples is U.S. Pat. No. 3,409,369, issued to G. W. Bickel and concerning a laser radar system which operates on the Doppler velocity measuring principle using two different transmitted frequencies in order to obtain a conveniently low difference frequency. Since the Bickel apparatus is principally concerned with the Doppler operating concept and target velocity measurement, the present invention is readily distinguished therefrom.
Also included in these prior patents is U.S. Pat. No. 3,465,156 issued to C. J. Peters and concerned with a laser communication system which employs a narrow band noise cancellation technique with the transmitted laser beam divided into two different paths. The Peters invention received laser light is also split into two beams one of which contains video signal modulation and both of which contain noise components. Since the Peters apparatus is concerned with a laser communication system, the present invention range mapping concepts are readily distinguished.
Also included in these prior patents is U.S. Pat. No. 3,504,182 issued to V. F. Piezzurro et al and concerned with an optical communication system. In the Piezzurro et al communication system scanning by the beam emitted from one station is used to "acquire" the scanning pattern of a second station in order that the two stations can lock-on and be ready to transmit and receive information. Distinctions between the present invention and the communications system of Piezzurro et al are readily apparent.
Also included in this art is the laser radar mapping system of F. K. Knight et al reported in Applied Optics, Vol. 28, pp. 2196-2198, June 1989. In this system, use is made of a streak camera to obtain range maps of objects at a distance. The Knight et al apparatus does not teach the use of an electromagnetic shutter encoding as in the present invention.
Also included in this art is the U.S. Pat. No. 4,515,472 of A. B. Welch which is concerned with an agile receiver for a scanning laser radar system. The Welch apparatus uses a receiver frequency adjustment arrangement in order to rapidly acquire, recognize, track and perform simultaneous guidance functions for a multiplicity of weapons against a multiplicity of targets. In view of this purpose and functioning of the Welch apparatus, distinction from the present invention range mapping system is easily discerned.